1) it's not. You can import data from Bento into FileMaker, but you can't just import the rest of your design into FileMaker.
2) You just re-install the application on your new computer and then copy over your database file.
3) No. There is no build in "Sync" capability. Out of the box, you can only copy files back and forth between the two devices. You'd either create your own, or acquire a third party tool such as those supplied by SeedCode and 360Works to do the synch. The other alternative is to keep your data on your computer and connect to it via wiFi or 4G so that your iOS device functions as a client of the database hosted by your computer. This requires keeping the databse open on your computer in FileMaker Pro or Server, setting up the needed connections settings (4G access is more complicated than WiFi) and then having a reliable connection to the hosted database.